We investigated phonological abilities, visual cognitive abilities, rapid automatized naming (RAN) and verbal long term memory in children with borderline intellectual functioning and reading/writing deficits (N = 50), using identical cognitive tasks used in previous studies. Most children showed deficits in phonological abilities, visual cognitive abilities and/or RAN, irrespective of their grade, and word comprehension level. These multiplex cognitive deficits were considered a core cognitive mechanism underlying their reading/writing deficits, which could be a possible cause of developmental dyslexia in Japanese children having normal general intellectual functioning. We also found that intact cognitive abilities in many children with developmental dyslexia including semantic comprehension of words and verbal long term memory were poor in some children with borderline intellectual functioning. These results suggest the importance of investigating intact cognitive abilities in educational practice research on the effects of reading and writing skills training.
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